fix(material/checkbox): add more prominent focus indication in high contrast mode
fix(material/checkbox): add more prominent focus indication in high contrast mode

Currently the checkbox only switches to a dotted border when it receives focus in high
contrast mode. These changes make it a bit more prominent by using a solid outline
on the ripple element.

josephperrott/material2,andrewseguin/material2,DevVersion/material2,andrewseguin/material2,crisbeto/material2,josephperrott/material2,mmalerba/material2,angular/components,andrewseguin/material2,crisbeto/material2,DevVersion/material2,DevVersion/material2,angular/components,angular/components,DevVersion/material2,andrewseguin/material2,crisbeto/material2,josephperrott/material2,angular/components,crisbeto/material2,josephperrott/material2,mmalerba/material2,mmalerba/material2,DevVersion/material2,josephperrott/material2,andrewseguin/material2,mmalerba/material2,mmalerba/material2